Over the Christmas holiday, quite a few of us will consume ethanol-containing products. This simple, two-carbon molecule is a potent (and legal) mood-altering drug that is woven into the fabric of European and many other cultures since time immemorial. Ethanol has been part of the furniture of human civilization since enterprising farmers discovered it in rotten fruit. It is only fitting that it features prominently at Christmas, a winter feast of excess.
Charles Darwin performed experiments on plant movements with his seventh child, Francis Darwin, which they wrote up as joint authors in 1880 (Francis was a young man at the time). Every year, thousands of children and budding scientists repeat these experiments:
- Shine a light on a plant from just one source, and observe as plants orientate their growth to ‘face’ the light.
- Adorn growing shoots with a ‘cap’ that is impermeable to light and observe as they grow straight, even as light hits the open stem.
The tip of the plant senses the direction of the light, and this information is transmitted to the growing stem to direct growth behaviour. That transmission is performed by auxins, the first of which was isolated in the 1930s.
No one could mistake the pungent, spicy smell of caraway on rye bread, or perhaps in a yoghurt pudding, for the sharp, fresh smell of spearmint pinched from the garden or flavouring your tea. The two are entirely distinct. And yet the chemicals that make these two smells are identical in every possible way, except that they are mirror images of each other (‘enantiomers’).
Chinese culture has long treated ailments using herbal extracts in intricate combinations. This oeuvre of herbal experimentation gave rise to purified forms more recognisable as medicines, of which Artemisinin is one success story.
One of the first fluorescent molecules to be synthesised by humans was Fluorescein. The imposing German chemist Adolf von Baeyer created it in 1871, and was awarded the 1905 Nobel Prize in Chemistry for his work on dyes and aromatic compounds.
My seventh chemical of Christmas is not routinely made in biology, and is actually lethal to most large animals. Crafted by extremely inventive chemists in the 19th Century, benzene is a beautifully symmetric molecule with 6 carbons and 6 hydrogens.
Ah, the smell of coffee brewing, of tea steaming, hot chocolate beckoning on a cold winter’s day… the fizzy kick of Coca-Cola on a long journey. It’s wonderful, really. The taste, feel and cultural significance of each of these drinks may differ, but they all share one key ingredient: caffeine. Caffeine is the most commonly used mood-altering drug for humans: it wakes us up, prepares our minds for work, keeps us alert (we think) and provides a shared experience during informal interactions.
One of the most important discoveries of the 20th Century was antibiotics: chemicals that kill bacteria but not their human hosts. It changed the shape of human society as people began to survive septic cuts, everyday horrific infectious diseases, syphilis and tuberculosis.
Preparations derived from willow have been a regular feature of the human medicine cabinet for centuries: Ancient Egyptians drank willow ‘tea’ to relieve pain, and the Classic Greek physician Hippocrates wrote about the remedy in 400 BC. But it took a team of German chemists in 1897, working for Bayer, to synthesise a pure compound related to the active substances in willow, acetylsalicylic acid. They packaged it up neatly in pill form, and sold it under its trademarked name, Aspirin, which quickly became a household word.
Small molecules can be great for sending biochemical signals between cells, or between different parts of a cell, because they can diffuse rapidly in water – notably, the water in your body. Big, multicellular organisms rely on hundreds of such molecules to get on with the business of living.